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Analysis A prof in California has made the unsurprising observation that you can produce more transport miles from an acre of cropland by growing biomass for generators and using electric vehicles than by burning crop biofuels in ordinary engines.

Assistant professor Elliott Campbell and his colleagues compared two different ways of using plants to power vehicles. The first method, already an option today, was to grow feedstocks such as corn or switchgrass and convert them into ethanol fuel.

Ethanol can be burned in ordinary cars with only minor modifications, which is one reason it has already gained some traction. Another is that powerful American and European farming lobbies hope that it could mean big money for them.

The second method considered by Campbell and his collaborators was to grow biomass and use this in generators to produce electricity - so-called "bioelectricity" - to charge the batteries of electric cars.

According to the researchers:

Bioelectricity outperforms ethanol across a range of feedstocks, conversion technologies, and vehicle classes. Bioelectricity produces an average 81% more transportation kilometers and 108% more emissions offsets per unit area cropland than cellulosic ethanol. These results suggest that alternative bioenergy pathways have large differences in how efficiently they use the available land to achieve transportation and climate goals.

This is hardly a surprise, though it has seemed startling enough to the media that it's gone mainstream. After all, conventional car engines of the sort used to burn ethanol put out barely 20 per cent of their fuel's energy at the drive shaft. By contrast, an electric motor can beat 80 per cent without trouble.

Of course there are other losses in the bioelectricity method - at the generator, in charging up batteries - but this is also true for making ethanol fuel out of crops, a process which requires a lot of heat energy to accomplish. It's not exactly startling that "bioelectricity" comes out somewhat ahead.

"We found that converting biomass to electricity rather than ethanol makes the most sense for two policy-relevant issues, transportation and climate," said Campbell. "We also need to compare these options for other issues such as water consumption, air pollution and economic costs."